In current CMOS scaling, the scaling of the physical channel length has not kept up with other scaling parameters. This issue has exacerbated several other scaling parameters, such as the distance between the metal contact and the gate.
A reverse short channel effect is a reduction in threshold voltage as the gate length increases. Namely, with CMOS devices, non-uniform channel doping is typically present where the source and drain regions of the device are more heavily doped (i.e., halo doping to reduce the depletion regions). As a result, in short channel length devices, the source and drain halo doping regions can overlap (also referred to as halo merging), thus increasing the overall channel dopant concentration as well as the threshold voltage. By comparison, in devices having a larger channel length, the source and drain halo doping are separated thus decreasing the overall channel dopant concentration as well as the threshold voltage.
To scale to shorter channel lengths, methods that enable adding a reverse short channel effect (such as occurs in planar bulk or partially depleted silicon-on-insulator (PDSOI) CMOS) would be highly beneficial.